Solar cells have a low output voltage as individual elements. Therefore, when they are applied, an appropriate solar cell module is prepared as necessary by configuring a solar cell cluster in which multiple solar cells are connected in series. In other words, a solar cell module is formed by connecting multiple solar cells in series, and there are cases where variation in the amount of light irradiation for some solar cells (e.g., a shaded area) has an influence on the solar cell module as a whole.
For example, if only some of the solar cells connected in series become shaded, an imbalance in the irradiated area arises between the series stages. If the irradiated area differs between solar cells, the output of the series-connected solar cells will be limited by the solar cell having the lowest irradiation amount (solar irradiation amount). In other words, even if the shaded area is small, all of the series-connected solar cells are affected, and there are cases where the output is greatly limited.
A known countermeasure for variation in the amount of light irradiation for solar cells is to connect a bypass diode in parallel with the solar cell. According to this countermeasure, a bypass current flows in a stage where there is low light irradiation (a stage where there is a large shaded area) because of the operation of the bypass diode, and even when the stage is partly illuminated by light irradiation, there is little contribution to the output. In addition, the voltage drop which occurs across the bypass diode leads to loss of electric power.
Furthermore, various techniques have been proposed as countermeasures for shaded areas (e.g., see Patent Documents 1 to 4,).
According to the technology disclosed in Patent Document 1, the direction of cross-pieces for fixing a roof member incorporating solar cell elements and the direction of the series connection of the solar cell elements are set parallel to each other so as to equalize the reduction in the output of the solar cell elements due to shadows created by the cross-pieces. This is a countermeasure for a very specialized mode of avoiding the influence of shadows created by cross-pieces used in installation, not a general countermeasure for variation in the amount of light irradiation, and therefore cannot be said to be a so-called countermeasure for shaded areas. Furthermore, other applications of this technology would be very difficult.
According to the technology disclosed in Patent Document 2, solar cell modules configured by solar cell elements are arranged in a vertically stepped manner, and the direction of the series connection of the solar cell elements is set to a direction orthogonal to the vertical direction. Although this prevents a problem from arising even if an upper solar cell module creates a shadow on a lower solar cell module, this is a countermeasure directed to solar cell modules that are arranged in a vertically stepped manner, and is for avoiding the influence of shadows created by the solar cell modules. This is not a general countermeasure for variation in the amount of light irradiation, and therefore cannot be said to be a so-called countermeasure for shaded areas. Furthermore, other applications of this technology would be very difficult.
According to the technology disclosed in Patent Document 3, the longitudinal direction of solar cells and the longitudinal direction of solar cell modules formed by arranging the solar cells are set so as to be orthogonal to each other so as to diminish a reduction in output due to a shadow created by a step portion when the solar cell modules are stacked in steps. This is not a general countermeasure for variation in the amount of light irradiation, and therefore cannot be said to be a so-called countermeasure for shaded areas. Furthermore, other applications of this technology would be very difficult.
According to the technology disclosed in Patent Document 4, the number of solar cell modules that are installed is set high in advance for solar cell arrays that are installed in places where shadows are created. This is not a general countermeasure for variation in the amount of light irradiation, and therefore cannot be said to be a so-called countermeasure for shaded areas. Furthermore, other applications of this technology would be very difficult.
Patent Document 1: JP H7-217087A
Patent Document 2: JP 2001-36125A
Patent Document 3: JP 2001-111083A
Patent Document 4: JP 2002-237612A